Leadless Semiconductor Packages

ABSTRACT

An encapsulation technique for leadless semiconductor packages entails: (a) attaching a plurality of dice ( 411 ) to die pads in cavities ( 41 - 45, 51 - 55 ) of a leadframe, the cavities arranged in a matrix of columns and rows; (b) electrically connecting the dice to a plurality of conducting portions ( 412 - 414 ) of the leadframe; and (c) longitudinally injecting molding material into the cavities along the columns via a plurality of longitudinal gates ( 46 - 49, 56 - 59 ) of the leadframe to package the dice in the cavities, the longitudinal gates situated between the cavities along the columns.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 10/789,799filed Feb. 27, 2004, which is a divisional of U.S. patent applicationSer. No. 10/113,526 Filed Mar. 28, 2002, and are both incorporatedherein by reference.

BACKGROUND OF THE INVENTION

Conventional encapsulation methods for packaging semiconductor devicesare classified into two kinds. The first encapsulation method is appliedto semiconductor packages with leads, as shown in FIG. 1. A plurality ofdice are respectively mounted in cavities 11 of a leadframe 1, and areconnected to the pins of the leadframe 1. The leadframe 1 has runner 12,and the runner 12 is connected to the cavities 11 by sub-runners 13 andgates 14. Each gate 14 is an injection inlet between a sub-runner 13 anda cavity 11. Molding material is injected into the runner 12 and movesvia the sub-runners 13 and the gates 14 to cavities 11 so as to packagethe dice in cavities 11. This encapsulation method requires space forthe runner 12 and the sub-runners 13, thereby decreasing the number ofdice within the leadframe area, and does not have high packagingefficiency.

The second encapsulation method is applied to leadless semiconductorpackages, as shown in FIG. 2. A plurality of dice 22 are placed in acavity 21. Molding material is injected into the cavity 21 to packagethe dice 22. Therefore, the number of dice within the leadframe isincreased, and the cost of the leadframe can be decreased. However, thesecond method must use cutting equipment to cut the packagedsemiconductor devices into individual pieces, and the cutting equipmentis usually expensive. Therefore, the cost of the second method is high.Furthermore, after the semiconductor devices are cut, every one of thesemiconductor devices must be transferred to a tray or a tube so thatthe steps of the second method are complex and the efficiency of thesecond method is low.

Besides, as shown in FIG. 3, each packaged semiconductor device 3 has nocontact leads. Instead, device 3 has a plurality of conducting portions31 for connection to a circuit board. When the leadless semiconductordevice 3 is packaged, molding flash must not remain on the conductingportions 31. Therefore, during the packaging process, a film at thebottom of the semiconductor device 3 is needed to prevent molding flashfrom remaining on the conducting portions 31. Such a film increases thecost of the second method and degrades the efficiency.

On the other hand, the second method must utilize an upper mold and alower mold to clamp the periphery of the leadframe 2, and the moldingmaterial is injected into the cavity 21 formed by the upper and lowermolds. Because the cavity 21 is large, the upper and lower molds canonly clamp the periphery of the lead frame 2. The middle portion of thecavity 21 cannot be clamped by the upper and lower molds. This willeasily cause molding flash to remain on the conducting portions 31.

Therefore, it is desirable to provide a creative and improvedencapsulation method and leadframe to overcome the above problems.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a leadframe forleadless semiconductor packages. The present leadframe comprises: aplurality of cavities and a plurality of longitudinal gates. Each cavityhas at least one die pad for supporting at least one die. Each cavityhas a plurality of conducting portions for electrical connection to thedie or dice on the die pad or pads. The cavities are arranged in amatrix configuration and classified into a plurality of columns and aplurality of rows. The longitudinal gates are situated between thecavities along the columns. Molding material is injected into thecavities along the columns via the longitudinal gates to package thedice in the cavities.

Therefore, the leadframe of the invention does not have the runner ofthe conventional leadframe, and can have more space to support moredice. The density of dice accommodated by the present leadframe can behigh, and the packaging efficiency can be improved. Besides, the moldingmaterial remaining in the runner can be minimized by using the leadframeof the invention so as to decrease the manufacturing cost.

Another objective of the invention is to provide an encapsulation methodfor leadless semiconductor packages. The method comprises the steps of:(a) attaching a plurality of dice to die pads in a plurality of cavitiesof a leadframe, the cavities arranged in a matrix configuration andclassified into a plurality of columns and a plurality of rows; (b)electrically connecting the dice on the die pads to a plurality ofconducting portions of the leadframe; and (c) longitudinally injectingmolding material into the cavities along the columns via a plurality oflongitudinal gates of the leadframe to package the dice in the cavities,the longitudinal gates situated between the cavities along the columns.

The method of the invention does not need a film to prevent moldingflash, and can solve the problem of molding flash remaining on theconducting portions. The method of the invention does not use expensivecutting equipment so as to decrease the cost and to upgrade theefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not by way oflimitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 shows a conventional leadframe for packaging semiconductordevices with leads.

FIG. 2 shows a conventional leadframe for packaging leadlesssemiconductor devices.

FIG. 3 shows a conventional leadless semiconductor device.

FIG. 4 shows a top-view of a leadframe for leadless semiconductorpackages according to the present invention.

FIG. 5 shows a flow chart illustrating an encapsulation method forleadless semiconductor packages according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the scope of the invention as defined by theappended claims. Furthermore, in the following detailed description ofthe present invention, numerous specific details are set forth in orderto provide a thorough understanding of the present invention. However,it is understood that the present invention may be practiced withoutthese specific details. In other instances, well-known methods,procedures, components, and circuits have not been described in detailas not to unnecessarily obscure aspects of the present invention.

Referring to FIG. 4, according to the invention, a leadframe 4 forleadless semiconductor packages comprises a plurality of cavities 41,42, 43, 44, 45, 51, 52, 53, 54, 55 and a plurality of inter-cavitylongitudinal gates 46, 47, 48, 49, 56, 57, 58, 59. Each cavity has a diepad (not shown in the figure) for supporting a die. Die 411 is, forexample, attached to its die pad in cavity 41. Each cavity has aplurality of conducting portions for electrical connection to the die onthe die pad. For example, the cavity 41 has three conducting portions412, 413 and 414. In the embodiment of the invention illustrated in FIG.4, each cavity has one die pad for supporting a die. To improve theefficiency, each cavity can have a plurality of die pads for supportinga plurality of dice.

The cavities are arranged in a matrix configuration, and are classifiedinto a plurality of columns and a plurality of rows. For example, thecavities 41, 42, 43, 44 and 45 form a first column, and the cavities 51,52, 53, 54 and 55 form a second column. The cavities along the directionof cavities 41 and 51 form a first row, and the cavities along thedirection of cavities 42 and 52 form a second row.

The inter-cavity longitudinal gates 46, 47 ,48, 49, 56, 57, 58 and 59are situated between the cavities along the columns. For example, thelongitudinal gate 46 is situated between cavity 41 and cavity 42 forconnecting the cavity 41 and the cavity 42. Similarly, the longitudinalgate 47 is situated between the cavity 42 and the cavity 43 forconnecting the cavity 42 and the cavity 43. Therefore, the cavities 41,42, 43, 44 and 45 are connected by the longitudinal gates 46, 47, 48 and49. Similarly, the cavities 51, 52, 53, 54 and 55 are connected by thelongitudinal gates 56, 57, 58 and 59.

Molding material is injected into the cavities along the columns of theleadframe 4 via the longitudinal gates to package the dice in thecavities. For example, firstly the molding material is injected into afirst longitudinal gate 40 of the first column, and then flows into thecavity 41 of the first column via the first longitudinal gate 40. Insequence, the molding material flows into the longitudinal gate 46, thecavity 42, the longitudinal gate 47, the cavity 43, the longitudinalgate 48, the cavity 44, the longitudinal gate 49, and the cavity 45 topackage the dice in the cavities along the first column.

The leadframe 4 of the invention does not have the runner 12 as shown inthe conventional leadframe 1 of FIG. 1, and the leadframe 4 can havemore space to support more dice. The density of dice accommodated by theleadframe 4 can be high, and the packaging efficiency can be improved.Besides, the molding material left in the runner can be minimized byusing the leadframe 4 of the invention so as to decrease themanufacturing cost.

According to the embodiment of the invention, to further improve thepackaging quality, the leadframe 4 further comprises a plurality oftransverse (or horizontal) gates 61, 62, 63, 64 and 65. The transversegates are situated between the cavities along the rows. For example, thehorizontal gate 61 is situated between the cavity 41 and the cavity 51for connecting the cavity 41 and the cavity 51. Similarly, thetransverse gate 62 is situated between the cavity 42 and the cavity 52for connecting the cavity 42 and the cavity 52. When the moldingmaterial is injected into the cavities along the columns, the moldingmaterial can flow into the transverse gates so as to balance thepressure between the cavities along the rows. The bubbles induced in thecavities by the molding material can be drained by the transverse gatesto further improve the packaging quality.

Referring to FIG. 5, the flow chart illustrates an encapsulation methodfor semiconductor packages according to the present invention. In step501, the dice are attached to the die pads in the cavities of theleadframe 4. The leadframe 4 has a plurality of cavities arranged in amatrix configuration and classified into a plurality of columns and aplurality of rows. In step 502, the dice are electrically connected tothe conducting portions of the leadframe 4.

In step 503, the molding material is injected longitudinally to packagethe dice. The molding material is injected into the cavities along thecolumns via the longitudinal gates to package the dice in the cavitiesalong the columns. The longitudinal gates are situated between thecavities along the columns.

In step 503, the molding material can flow into the transverse gates soas to balance the pressure between the cavities along the rows and todrain the bubbles induced in the cavities by the molding material. Thetransverse gates are situated between the cavities along the rows.

The method of the invention does not need a film to prevent flash, andcan solve the problem of molding flash remaining on the conductingportions. The method of the invention does not use expensive cuttingequipment so as to decrease the cost and to upgrade the efficiency.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

1. A semiconductor comprising: a portion of a leadframe; a given die;and a portion of a molding material; wherein the semiconductor is formedby; attaching a plurality of dice to die pads in a plurality of cavitiesof the leadframe, the cavities arranged in a matrix of columns and rows,wherein the plurality of dice include the given die; electricallyconnecting the dice to a plurality of conducting portions of theleadframe; causing a molding material to flow into a first cavity;causing said molding material to flow from said first cavity into asecond cavity adjacent to and in the same column as said first cavitythrough a first gate of the leadframe that is separately connectedbetween said first cavity and said second cavity; and causing saidmolding material to flow from said first cavity into a third cavityadjacent to and in the same row as said first cavity through a secondgate of the leadframe that is separately connected between said firstcavity and said third cavity.
 2. The semiconductor of claim 1, whereinthe semiconductor is further formed by causing said molding material toflow from said first cavity into a fourth cavity adjacent to and in thesame row as said first cavity.
 3. The semiconductor of claim 1, whereinthe semiconductor is further formed by: causing said molding material toflow from said second cavity into a fourth cavity adjacent to and in thesame column as said first cavity; and causing said molding material toflow from said second cavity into a fifth cavity adjacent to and in thesame row as said second cavity.
 4. An article formed by a processcomprising: attaching a plurality of dice to die pads in a plurality ofcavities of a leadframe, wherein the cavities are arranged in a matrixhaving a plurality of columns of cavities and a plurality of rows ofcavities; injecting a molding material along each of the plurality ofcolumns of cavities through a first plurality of gates of saidleadframe, wherein each gate of said first plurality of gates isseparately connected between corresponding adjacent cavities of saidplurality of columns of cavities; causing the molding material to flowalong each of the plurality of rows of cavities through a secondplurality of gate of said leadframe, wherein each gate of said secondplurality of gates is separately connected between correspondingadjacent cavities of said plurality of rows of cavities; and separatingthe plurality of dice, the leadframe and molding material into aplurality of semiconductor devices after injecting and causing themolding material to flow, wherein each semiconductor device include oneof the plurality of die, a portion of the leadframe and a portion of themolding material.
 5. The article formed by a process according to claim4, wherein causing the molding material to flow along each of theplurality of rows of cavities balances a pressure of the moldingmaterial injected along each of the plurality of columns of cavities. 6.The article formed by a process according to claim 4, wherein causingthe molding material to flow along each of the plurality of rows ofcavities drains bubbles induced in the molding material in the pluralityof cavities.
 7. The article formed by a process according to claim 4,further comprising electrically connecting the dice to a plurality ofconducting portions of the leadframe before injecting the moldingmaterial.
 8. The article formed by a process according to claim 4,wherein the molding material flows along each of the plurality of rowsof cavities in response to injecting the molding material along each ofthe plurality of columns of cavities.
 9. An article comprising: aleadframe including a plurality of cavities arranged in a matrix and aplurality of gates between the plurality of cavities, a plurality of dieeach disposed in a respective cavity; molding material; wherein thearticle if formed by a process comprising: injecting a molding materialinto a first cavity of the plurality of cavities, from the first cavitythrough a first gate of the plurality of gates into a second cavity andfrom the second cavity through a second gate into a third cavity,wherein the first cavity, the second cavity and the third cavity aresituated along a first column of the matrix, and wherein the first gateis separately connected between the first cavity and second cavity, andthe second gate is separately connected between the second cavity andthird cavity; injecting the molding material into a fourth cavity, fromthe fourth cavity through a third gate into a fifth cavity and from thefifth cavity through a fourth gate into a sixth cavity, wherein thefourth cavity, the fifth cavity and the sixth cavity are situated alonga second column, and wherein the third gate is separately connectedbetween the fourth cavity and fifth cavity, and the fourth gate isseparately connected between the fifth cavity and sixth cavity; andcausing the molding material to flow from the second cavity through afifth gate into the fifth cavity, wherein the fifth gate is separatelyconnected between the second cavity and fifth cavity situated along arow of the matrix containing the second cavity and fifth cavity.
 10. Thearticle formed by a process according to claim 9, wherein the moldingmaterial flows from the second cavity through the fifth gate into thefifth cavity in response to injecting the molding material along thefirst column and the second column.
 11. The article formed by a processaccording to claim 10, wherein causing the molding material to flow fromthe second cavity through the fifth gate into the fifth cavity inresponse to injection the molding material along the first column andthe second column is adapted to balance pressure between cavities in thefirst column and cavities in a second column.
 12. The article formed bya process according to claim 10, wherein causing the molding material toflow from the second cavity through the fifth gate into the fifth cavityin response to injection the molding material along the first column andthe second column is adapted to drain bubbles induced in the moldingmaterial.
 13. The article formed by a process according to claim 10,further comprising electrically connecting the dice to a plurality ofconducting portions of the leadframe before injecting the moldingmaterial.